Amateur-built RotorWay RW 1 N166LC accident near Billings, Montana

Probable cause

The pilot's failure to maintain clearance with a hangar while maneuvering to his hangar. Contributing to the accident was the pilot's limited experience in helicopters.

NTSB analysis

The pilot, who did not hold a helicopter rating, was maneuvering his experimental amateur-built helicopter around the airport area. An acquaintance of the pilot stated that the accident pilot would regularly hover-taxi around the airport area testing the helicopter. The acquaintance also stated that, on the day of the accident, the pilot mentioned that the helicopter was flying well and that he did not have any issues with it. Afterward, the pilot started the helicopter and departed to the west and hover-taxied around the row of hangars back to his hangar. The acquaintance reported that he did not see the accident but that he heard the sound of the helicopter impacting a hangar.

Postaccident examination of accident site showed that the helicopter's main rotor blades had collided with the top section of the hangar and that the helicopter came to rest oriented upward on an angle of about 30° and against the front of the hangar on a westerly heading. It is likely that, during the hover-taxi, the accident pilot ascended above a hover to the height of the hangars before colliding with one.

The left anti-torque pedal for the pilot's right-seat position had failed where the horizontal and vertical tubes met. Notwithstanding the failed anti-torque pedal, examination of the airframe and engine found no mechanical anomalies that would have precluded normal operation of the helicopter.

A metallurgical examination of the fractured horizontal and vertical components of the pilot's right seat's left anti-torque pedal assembly revealed that they failed from a lack of complete fusion at a fillet joint, which led to an overstress fracture. The fractured pedal tube assembly consisted of two aluminum tubes joined together with a filler metal that was consistent with a zinc solder alloy. However, the right anti-torque pedal tube assembly, which was intact, consisted of alloy steel tubes that were welded together with an alloy steel filler metal. The intact tube assembly had a much stronger quality due to the welding process and the inherent higher mechanical properties of the steel than those of the fractured tube assembly.

A build ledger for the helicopter revealed that the anti-torque pedals had been fabricated in December 1996 by the previous owner, almost 20 years before the accident pilot purchased the helicopter. However, the ledger did not detail the fabrication differences among the anti-torque pedals.

The investigation could not determine if the left anti-torque pedal for the right-seat position failed before the impact with the hangar or during the impact sequence. Although the pilot might have been able to control the helicopter after the pedal failed, that possibility would be unlikely given the pilot's minimal experience in helicopters.

Text from the NTSB. Open the NTSB docket for WPR18FA260 for the full record.